by.im {spatstat} | R Documentation |
Splits a pixel image into sub-images and applies a function to each sub-image.
## S3 method for class 'im': by(data, INDICES, FUN, ...)
data |
A pixel image (object of class "im" ). |
INDICES |
Grouping variable.
Either a tessellation (object of class "tess" ) or
a factor-valued pixel image.
|
FUN |
Function to be applied to each sub-image of data . |
... |
Extra arguments passed to FUN . |
This is a method for the generic function by
for
pixel images (class "im"
).
The pixel image data
is first divided into sub-images according
to INDICES
. Then the function FUN
is applied to each subset.
The results of each computation are returned in a list.
The grouping variable INDICES
may be either
"tess"
). Each tile of
the tessellation delineates a subset of the spatial domain.
"im"
) with factor
values. The levels of the factor determine subsets of the spatial
domain.
A list containing the results of each evaluation of FUN
.
Adrian Baddeley adrian@maths.uwa.edu.au http://www.maths.uwa.edu.au/~adrian/ and Rolf Turner r.turner@auckland.ac.nz
W <- square(1) X <- as.im(function(x,y){sqrt(x^2+y^2)}, W) Y <- dirichlet(runifpoint(12, W)) # mean pixel value in each subset unlist(by(X, Y, mean)) # trimmed mean unlist(by(X, Y, mean, trim=0.05))